Last updated: December 6, 2022
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Twin brothers recently visited our farm to look at a horse; their stop-over inspired my grandson to ask if horses can have twins or triplets. I’ve never owned a broodmare that delivered multiple foals, so I decided to research the topic.
Horses can have twins, but it’s rare, and typically one or both are lost during pregnancy. There are instances of horses conceiving and delivering triplets, but live births are extraordinarily uncommon, about 1 in every 300,000 births.
Horse breeders want their mare to have healthy foals, and the more, the better. But learning their mare is in foal to twins or triplets isn’t typically well received.
Healthy twins are rare in horses.
A mare conceiving twins isn’t exceedingly rare, however, delivering healthy twin foals is. Approximately 1 in 10,000 horse births are twins, compared to 3 in every 100 for humans.
There are numerous reasons for the scarcity of equine twins. First and foremost is that the mare frequently miscarries either one or both babies within the first six weeks of pregnancy.
Spontaneous abortions and reabsorptions occur because there isn’t room for both foals, and they don’t get enough nutrition. An equine embryo needs space to position itself to gain valuable oxygen and nutrients, and two embryos just don’t have enough room.
The embryos are in a mare’s uterus, and they move around between the uterine horns. There is limited space in the uterus horns for both embryos. Because of the insufficient area, one or both of the babies in the placenta die from starvation.
If the embryo passes within the first six weeks of pregnancy, spontaneous resorption is likely. Embryos that survive past this point are still highly likely to be lost before birth. Late-term miscarriages are dangerous for the mother and can leave her barren.
Successfully born twins typically survived by traveling to a safe area in the womb to develop, but they still competed with their siblings for nutrition. Scarce nutrients are a primary reason twin foals are born smaller than single foals.
Horse owners typically check their mares soon after breeding to confirm conception and find out if they are carrying multiple babies. They do this so they can terminate one of the embryos before it gets too large and damages either the mare or its twin.
There are high risks in delivering twins.
When a mare does deliver twins, foaling problems often occur, and she is at risk of death. Ideally, the foals come out one after the other, but that’s not always the case.
sometimes both foals try to exit the womb simultaneously, as you can imagine, this creates serious problems. After the delivery of twins, many mares retain their placenta, which is a severe condition and can be fatal.
So, not only are the foals at risk, but the mother is as well. Another issue is that twins are typically born unhealthy and smaller than single-birthed foals.
Then the issue of nursing arises; if you don’t have a nurse mare to put one of the foals on, you may need to supplement the babies. This isn’t typically a big problem, but it is an issue to consider.
In the best scenario, the twins are born healthy, and the mare lives, but she will have a long recovery and need a break before breeding for the next season.
An ultrasound is used to detect twins.
Most horse owners have their veterinarian check their pregnant mare about two weeks after breeding and again after one month. The examination is not only to confirm conception but also to detect twins.
Don’t wait too long before having your mare examined; twins are much harder to verify after 60 days. A mobile ultrasound is part of most horse veterinarians’ equipment.
It is small affordable, and easily portable. And because of the advancements to mobile ultrasounds, they have almost a 100 percent detection rate.
It’s critical to find out if your mare is carrying twins as soon as possible. If twins are detected within the first two to three weeks, one can be aborted to give the other embryo a chance to be carried to term normally.
Most twins not aborted are born premature, typically between five and seven months, and neither fetus usually survives. However, some horses buck the trend.
Interesting twins: Mr. Ping and Mr. Pong are Thoroughbred twins that thrived. They not only were born healthy but beat the odds even further and made it to the racetrack.
They weren’t successful on the track, but to be strong enough to compete is a fantastic story. The pair was retired to the polo fields where twin brothers ride them.
Horses can have triplets.
In 1986 a buckskin mare in California gave birth to triplets, two fillies, and one colt. It seems the birth took place naturally in a field, and the family was quickly ushered to UC Davis school of medicine.
The family was doing fine upon the last report. The foals weighed between 35 and 28 pounds at birth, which is small but not terribly so. A typical foal weighs about 50 pounds.
The chances of a mare delivering triplets are 1-300,000, even having three embryos is extremely rare. Some estimates are that one out of 75-80 horses has two eggs fertile during its pregnancy, having three fertile eggs during a single gestation period is so rare I couldn’t find a figure.
Some horse breeds are more likely to have twins.
Certain horse breeds ovulate more than other breeds, which in turn results in more twin pregnancies. Three types that have the highest chances of twinning are Thoroughbreds, Standardbreds, and Warmbloods.
These horse breeds tend to have multiple ovulation, resulting in the fertilization of more than one egg. When this happens, the mare carries twins.
In some of these breeds, twinning occurs in thirty percent of their pregnancies are twins. This rate is exceptionally high when compared to most other horses.
Besides the type of horse, other factors result in multiple ovulations, such as whether the mare is lactating. Mares not nursing a foal at the time of breeding has a higher likelihood of double ovulating.
Horses that have carried twins in the past are also more prone to have multiple ovulations.
How many foals can a horse have?
Mares are fertile at about two years old and can reproduce into their late twenties. Their gestation period is eleven months, but they need a couple of months after delivery between breedings.
You can expect a mare to produce a foal approximately every eighteen months. But in most cases, a broodmare has its first baby as a five-year-old and continues to deliver foals until she reaches 23 years old.
Mares are at their peak fertility at approximately six years old. When they reach fifteen years old, their fertility begins to decline, and they are more challenging to get in foal, and are more likely to lose their baby.
After a mare reaches twenty-three, I consider her to be done as a broodmare. It’s not impossible for most to continue to conceive, and it’s just that the risks to the horse and foal are too significant to continue breeding.
If all goes well and she has standard breaks, you can expect her to have 13 foals over her lifetime. Most registered breeds use January 1 as the birthday for all foals born during the year.
As you know, mares can deliver a foal approximately every eighteen months, which means each proceeding foal is born later in the year. A breeder wants their foals born in the spring, so they often give a mare a break when her foaling period approaches summer.
The mare likely needs a break anyway. If a broodmare is appropriately taken care of, she will remain healthy and have no adverse effects from having many foals over her lifetime.
I expect a mare to have her last foal about 23 years old; after this age, horses’ fertility levels are low, and risks are high.
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